Hi to all. I have built a power supply using a uc3843 chip and need some help. The supply takes 220Vac and steps it down to 14Vdc(approx). I have managed to get the supply working OK , but I still need a bit of help.The schematic is attached , in LTSpice format.I modeled the schematic and it seems to be ok , but I'm not sure how much you can trust a simulation it this sort of level. I've attached the model file for anyone who would like to simulate the schematic. Hope it does not make the file to big , but I don't have any access to any other binary groups to send it to.
When I first powered up the circuit the output was very noisy , and got worse as the load increaced.I found by lots of trial and error that if I put a small(100pF) cap across R11(3k3) the output stabilizes and everything seems good.There is a bit of high frequency noise on the output at the switching frequency , but I am sure this is to be expected. Now the problem...
I found by checking the drive to the FET that the loop seems unstable at certain loads.As I increace the load from 0A to 2.5A you can see the gate drive pulse width increacing as expected , but at certain loads it seems to jump all over the place and the scope can't trigger.From about 300mA to say 1,5A the gate drive is a mess , and after that it seems to settle down nicely.
How do I go about fixing this.It does not seem to be causing a problem on the output , but I would like to fix it up anyway. I am sure it is a loop/compensation problem , but I am not sure how to go about fixing it.I have tried changing the gain resistor(R5) to 100k and 147K to no avail.Same with the compensation cap C2(100p / 200p). I have also fiddled with the resistor/cap combination around the TL431 , also without much luck. I am not very experienced with this type of power supply , so I am in the dark a bit!! It may also be a board layout problem.I did the board in a hurry and did not pay HUGE amount of attention to layout , but I did try and keep high current areas away from control lines etc.It is single sided. This is a sort of hobby project , so time is not really of the esscence. I only have a scope and meter to work with , so any solutions that involve using other expensive equipment will be out of my capability.My maths is also not very hot , so any solution that involve lots of complex maths may be beyound me , but post them anyway as the may be of interest to someone else.(they will be of interest to me , even if over my head!!)
Any help would be appreciated. Cheers Rob.
Here is the cct , and the model/symbol also follow.(hope that is everything)
Version 4 SHEET 1 1916 688 WIRE -720 384 -720 256 WIRE -592 176 -720 176 WIRE -592 208 -592 176 WIRE -528 144 -528 -144 WIRE -528 624 -528 272 WIRE -464 384 -720 384 WIRE -464 384 -464 208 WIRE -288 192 -320 192 WIRE -288 288 -288 272 WIRE -288 320 -368 320 WIRE -288 624 -528 624 WIRE -288 624 -288 384 WIRE -256 192 -288 192 WIRE -176 288 -176 272 WIRE -160 320 -288 320 WIRE -160 448 -160 400 WIRE -160 464 -160 448 WIRE -160 624 -288 624 WIRE -160 624 -160 528 WIRE -96 192 -176 192 WIRE -96 288 -176 288 WIRE -96 288 -96 256 WIRE -80 448 -160 448 WIRE -80 448 -80 384 WIRE -32 192 -96 192 WIRE -32 256 -96 256 WIRE -32 320 -160 320 WIRE -32 384 -80 384 WIRE -16 320 -32 320 WIRE 0 -144 -528 -144 WIRE 0 -128 0 -144 WIRE 0 -48 0 -64 WIRE 112 624 -160 624 WIRE 112 640 112 624 WIRE 128 128 128 32 WIRE 128 448 128 432 WIRE 128 624 112 624 WIRE 128 624 128 448 WIRE 144 -144 0 -144 WIRE 144 -32 144 -64 WIRE 144 32 128 32 WIRE 144 32 144 -32 WIRE 352 -32 144 -32 WIRE 352 48 352 32 WIRE 352 352 288 352 WIRE 352 400 352 352 WIRE 352 496 352 400 WIRE 352 624 128 624
Here is the uc384x models:
*=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D- UC3842B
- ON Semiconductor
- PWM Controller
- This model was developed for ON Semiconductor by:
- AEI Systems, LLC
- 5777 W. Century Blvd. Suite 876
- Los Angeles, California 90045
- Copyright 2002, all rights reserved.
- This model is subject to change without notice.
- Users may not directly or indirectly re-sell or
- re-distribute this model. This model may not
- be used, modified, or altered
- without the consent of ON Semiconductor.
- For more information regarding modeling services,
- model libraries and simulation products, please
- call AEi Systems at (310) 863-8034, or contact
- AEi by email: snipped-for-privacy@aeng.com. formatting link
- Revision: 1.0
- PSpice translation by Christophe Basso, snipped-for-privacy@onsemi.com
- .SUBCKT UC3842B 3 14 15 1 18 4 20 2
- E/A FDBK IS RT/CT GND OUT VC VREF
- UC3843B
- ON Semiconductor
- PWM Controller
- This model was developed for ON Semiconductor by:
- AEI Systems, LLC
- 5777 W. Century Blvd. Suite 876
- Los Angeles, California 90045
- Copyright 2002, all rights reserved.
- This model is subject to change without notice.
- Users may not directly or indirectly re-sell or
- re-distribute this model. This model may not
- be used, modified, or altered
- without the consent of ON Semiconductor.
- For more information regarding modeling services,
- model libraries and simulation products, please
- call AEi Systems at (310) 863-8034, or contact
- AEi by email: snipped-for-privacy@aeng.com. formatting link
- Revision: 1.0
- PSpice translation by Christophe Basso, snipped-for-privacy@onsemi.com
- .SUBCKT UC3843B 3 14 15 1 18 4 20 2
- E/A FDBK IS RT/CT GND OUT VC VREF
- UC3844B
- ON Semiconductor
- PWM Controller
- This model was developed for ON Semiconductor by:
- AEI Systems, LLC
- 5777 W. Century Blvd. Suite 876
- Los Angeles, California 90045
- Copyright 2002, all rights reserved.
- This model is subject to change without notice.
- Users may not directly or indirectly re-sell or
- re-distribute this model. This model may not
- be used, modified, or altered
- without the consent of ON Semiconductor.
- For more information regarding modeling services,
- model libraries and simulation products, please
- call AEi Systems at (310) 863-8034, or contact
- AEi by email: snipped-for-privacy@aeng.com. formatting link
- Revision: 1.0
- PSpice translation by Christophe Basso, snipped-for-privacy@onsemi.com
- .SUBCKT UC3844B 3 14 15 1 18 4 20 2
- E/A FDBK IS RT/CT GND OUT VC VREF
- V(50,18) > 2.5, 10, 0 ) } .ENDS
- UC3845B
- ON Semiconductor
- PWM Controller
- This model was developed for ON Semiconductor by:
- AEI Systems, LLC
- 5777 W. Century Blvd. Suite 876
- Los Angeles, California 90045
- Copyright 2002, all rights reserved.
- This model is subject to change without notice.
- Users may not directly or indirectly re-sell or
- re-distribute this model. This model may not
- be used, modified, or altered
- without the consent of ON Semiconductor.
- For more information regarding modeling services,
- model libraries and simulation products, please
- call AEi Systems at (310) 863-8034, or contact
- AEi by email: snipped-for-privacy@aeng.com. formatting link
- Revision: 1.0
- PSpice translation by Christophe Basso, snipped-for-privacy@onsemi.com
- .SUBCKT UC3845B 3 14 15 1 18 4 20 2
- E/A FDBK IS RT/CT GND OUT VC VREF
- V(50,18) > 2.5, 10, 0 ) } .ENDS
- VREF INV OUT V- .MODEL QPMOD PNP .MODEL DCLAMP D (RS=3D10 BV=3D5 IBV=3D.01) .MODEL DMOD D R1 10 4 100K R2 10 20 100K R3 6 20 316MEG C1 6 20 15.9P E1 5 20 6 20 1 R4 1 20 8MEG I2 4 9 .8M D12 9 4 DMOD R6 20 3 300 D11 9 12 DMOD Q1 20 13 12 QPMOD I3 13 20 68U D14 3 13 DMOD D15 20 6 DCLAMP L1 2 3 10U C2 3 20 200P R9 5 2 5 C5 2 20 .02U G1 20 6 10 1 100U .ENDS
- +V -V IN OUT .MODEL QMOD NPN RC=3D1.5 RE=3D.5 RB=3D100 IKF=3D0.5 CJC=3D0.4P .MODEL QMOD2 NPN TF=3D400P TR=3D400P .MODEL QIN NPN BF=3D100 BR=3D2 IS=3D1E-16 VAF=3D50
- CJE=3D1.5P CJC=3D.15P TR=3D1N TF=3D4N .MODEL DMOD D RS=3D1 IS=3D0.4U I3 4 8 100U D3 8 4 DMOD D4 12 8 DMOD Q3 8 1 9 QIN Q4 12 9 7 QMOD Q5 4 8 6 QMOD I4 7 1 .9M R1 3 2 10K Q8 1 2 7 QIN Q2 4 6 12 QMOD2 .ENDS
- CLK D R S QB Q X1 7 4 2 8 NAND3_0 X2 8 3 10 9 NAND3_0 X3 1 8 10 7 NAND3_1 X4 4 9 1 10 NAND3_0 X5 4 7 6 5 NAND3_1 X6 5 10 3 6 NAND3_0 X7 11 4 INV X8 12 3 INV .ENDS FFLOP
- .SUBCKT NAND3_0 1 2 3 4 E1 5 0 VALUE =3D { IF ( (V(1)>800mV) & (V(2)>800mV) & (V(3)>800mV), 0, 5 ) } R1 5 4 400 C1 4 0 20P IC=3D0 .ENDS NAND3_0
- .SUBCKT NAND3_1 1 2 3 4 E1 5 0 VALUE =3D { IF ( (V(1)>800mV) & (V(2)>800mV) & (V(3)>800mV), 0, 5 ) } R1 5 4 400 C1 4 0 20P IC=3D5 .ENDS NAND3_1
- .SUBCKT INV 1 2 E1 3 0 VALUE =3D { IF ( V(1)>800mV, 0, 5 ) } R1 3 2 100 C1 2 0 10P IC=3D5 .ENDS INV
- .SUBCKT SWhyste NodeMinus NodePlus Plus Minus PARAMS: RON=3D1 ROFF=3D1MEG VT=3D5 VH=3D2 S5 NodePlus NodeMinus 8 0 smoothSW EBcrtl 8 0 Value =3D { IF ( V(plus)-V(minus) > V(ref), 1, 0 ) } EBref ref1 0 Value =3D { IF ( V(8) > 0.5, {VT-VH}, {VT+VH} ) } Rdel ref1 ref 100 Cdel ref 0 100p IC=3D{VT+VH} Rconv1 8 0 10Meg Rconv2 plus 0 10Meg Rconv3 minus 0 10Meg .model smoothSW VSWITCH (RON=3D{RON} ROFF=3D{ROFF} VON=3D1 VOFF=3D0) .ends SWhyste
- ISOLATOR A C COL EMITTER RB 4 0 100Meg VM 1 6 D1 6 2 LED H1 7 0 VM .0055 R1 7 8 1K C1 8 0 3.35nF G1 3 4 8 0 1 Q1 3 4 5 MPSA06 .MODEL LED D(N=3D1.7 RS=3D.7 CJO=3D23.9P IS=3D85.3p BV=3D6 IBV=3D10U
- VJ=3D0.75 M=3D0.333 TT=3D4.32U) .MODEL MPSA06 NPN (IS=3D15.2F NF=3D1 BF=3D589 VAF=3D98.6 IKF=3D90M ISE=3D3.=
- BR=3D4 NR=3D1 VAR=3D16 IKR=3D0.135 RE=3D0.343 RB=3D1.37 RC=3D0.137 XTB=3D=
- CJE=3D9.67P VJE=3D1.1 MJE=3D0.5 CJC=3D7.34P VJC=3D0.3 MJC=3D0.3 TF=3D10.2=
- is=3D 4.41547e-06
- rs=3D 0.103922
- n=3D 1.03751
- tt=3D 1e-12
- cjo=3D 1.598e-10
- vj=3D 0.4934
- m=3D 0.4258
- eg=3D 0.6
- xti=3D 3.29768
- fc=3D 0.5
- bv=3D 48
- ibv=3D 0.01
- kf=3D 0
- af=3D 1
- CJO=3D45P VJ=3D.75 M=3D.302
- TT=3D50.4N BV=3D34V IBV=3D1MA .ENDS
- 10 =3D Drain 20 =3D Gate 30 =3D Source
--------------------------------
- PACKAGE INDUCTANCE
- LDRAIN 10 11 4.5e-09 LGATE 20 21 7.5e-09 LSOURCE 30 31 7.5e-09
- RESISTANCES
- RDRAIN1 4 11 RDRAIN 6.853 RDRAIN2 4 5 RDRAIN 0.088 RSOURCE 31 6 RSOURCE 0.1 RDBODY 8 30 RDBODY 0.061
- RGATE 21 2 5
------------------------------
- DBODY 8 11 DBODY DGD 3 11 DGD CGDMAX 2 3 3e-10 RGDMAX 2 3 1e+08 CGS 2 6 2.2e-10
--------------------------------------
- M1 5 2 6 6 MAIN
- .MODEL RDRAIN RES (
- .MODEL RSOURCE RES (
- .MODEL RDBODY RES (
- .MODEL MAIN NMOS (
- .MODEL DGD D (
- .MODEL DBODY D (
WIRE 352 624 352 560 WIRE 416 -32 352 -32 WIRE 416 400 352 400 WIRE 448 224 288 224 WIRE 496 48 352 48 WIRE 496 80 496 48 WIRE 512 48 496 48 WIRE 512 48 512 32 WIRE 640 -32 480 -32 WIRE 640 48 512 48 WIRE 688 224 528 224 WIRE 736 -144 144 -144 WIRE 736 -112 736 -144 WIRE 736 144 736 -32 WIRE 736 400 496 400 WIRE 736 400 736 240 WIRE 736 464 736 400 WIRE 736 624 352 624 WIRE 736 624 736 544 WIRE 864 448 864 432 WIRE 864 528 864 512 WIRE 864 544 864 528 WIRE 896 432 864 432 WIRE 912 544 864 544 WIRE 912 544 912 448 WIRE 944 -32 864 -32 WIRE 960 48 864 48 WIRE 960 80 960 48 WIRE 960 432 960 400 WIRE 960 480 960 432 WIRE 960 528 960 480 WIRE 960 624 960 608 WIRE 992 480 960 480 WIRE 1024 448 912 448 WIRE 1024 448 1024 400 WIRE 1024 528 1024 512 WIRE 1024 624 960 624 WIRE 1024 656 1024 624 WIRE 1056 -32 1008 -32 WIRE 1056 -16 1056 -32 WIRE 1056 48 960 48 WIRE 1072 528 1024 528 WIRE 1072 624 1024 624 WIRE 1088 -32 1056 -32 WIRE 1088 528 1072 528 WIRE 1184 -32 1168 -32 WIRE 1184 -16 1184 -32 WIRE 1184 48 1056 48 WIRE 1248 -32 1184 -32 WIRE 1248 -32 1248 -112 WIRE 1248 48 1184 48 WIRE 1312 -112 1248 -112 WIRE 1312 528 1264 528 WIRE 1312 528 1312 384 WIRE 1344 -112 1312 -112 WIRE 1344 -64 1344 -112 WIRE 1344 16 1344 0 WIRE 1344 48 1248 48 WIRE 1344 48 1344 16 WIRE 1344 592 1264 592 FLAG 112 640 0 FLAG 0 -48 0 FLAG 496 80 0 FLAG 960 80 0 FLAG 1344 592 Vfb FLAG -320 192 Vfb FLAG 1024 656 0 FLAG 1312 -112 Vout FLAG -368 320 Vref FLAG 1312 384 Vref FLAG -288 288 0 FLAG 1056 -32 Vsense FLAG 1024 320 Vsense FLAG 960 320 Vout SYMBOL UC3845B 128 288 R0 SYMATTR InstName U1 SYMATTR Value UC3842B SYMBOL res -176 304 R0 SYMATTR InstName R1 SYMATTR Value 15k SYMBOL res 512 384 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL cap -176 464 R0 SYMATTR InstName C1 SYMATTR Value 1n SYMBOL cap -112 192 R0 SYMATTR InstName C2 SYMATTR Value 220p SYMBOL res -192 176 R0 SYMATTR InstName R5 SYMATTR Value 47k SYMBOL res 720 448 R0 SYMATTR InstName R6 SYMATTR Value 0.22 SYMBOL cap 336 496 R0 SYMATTR InstName C3 SYMATTR Value 470p SYMBOL res 544 208 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R7 SYMATTR Value 22 SYMBOL res 128 -160 R0 SYMATTR InstName R8 SYMATTR Value 100k SYMBOL cap -16 -128 R0 SYMATTR InstName C4 SYMATTR Value 100=B5 SYMATTR SpiceLine Rser=3D0.1 SYMBOL ind2 720 -128 R0 SYMATTR InstName L1 SYMATTR Value 500=B5 SYMATTR Type ind SYMBOL ind2 624 64 M180 WINDOW 0 36 80 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName L2 SYMATTR Value 15=B5 SYMATTR Type ind SYMBOL schottky 480 -48 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D3 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 336 -32 R0 SYMATTR InstName C5 SYMATTR Value 68=B5 SYMATTR SpiceLine Rser=3D0.1 SYMBOL ind2 880 64 R180 WINDOW 0 36 80 Left 0 WINDOW 3 49 40 Left 0 SYMATTR InstName L3 SYMATTR Value 15=B5 SYMATTR Type ind SYMBOL schottky 944 -16 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D4 SYMATTR Value MBR735 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 1040 -16 R0 SYMATTR InstName C7 SYMATTR Value 220=B5 SYMATTR SpiceLine V=3D25 Rser=3D0.05 MTBF=3D1000 Lser=3D0 ppPkg=3D1 SYMBOL voltage -720 160 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR SpiceLine Rser=3D1 SYMATTR InstName V1 SYMATTR Value SINE(0 311 50) SYMBOL ind 1184 -48 R90 WINDOW 0 5 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName L4 SYMATTR Value 10=B5 SYMATTR SpiceLine Rser=3D0.01 SYMBOL cap 1168 -16 R0 SYMATTR InstName C6 SYMATTR Value 470=B5 SYMATTR SpiceLine V=3D25 Rser=3D0.05 MTBF=3D1000 Lser=3D0 ppPkg=3D1 SYMBOL res 1232 -48 R0 SYMATTR InstName R10 SYMATTR Value 14 SYMBOL Optos\\\\4N25 1168 592 R0 SYMATTR InstName U4 SYMBOL mystuff\\\\my\\ nmos 688 144 R0 SYMATTR InstName U5 SYMATTR SpiceModel irfbe30 SYMBOL mystuff\\\\tl431 1008 448 R0 SYMATTR InstName U7 SYMBOL res 944 512 R0 SYMATTR InstName R11 SYMATTR Value 3.3k SYMBOL res 1008 304 R0 SYMATTR InstName R13 SYMATTR Value 2.2k SYMBOL res 944 304 R0 SYMATTR InstName R14 SYMATTR Value 10k SYMBOL cap 960 416 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C9 SYMATTR Value 220n SYMBOL res 848 432 R0 SYMATTR InstName R17 SYMATTR Value 1k SYMBOL res -304 176 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -160 176 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL cap -304 320 R0 SYMATTR InstName C8 SYMATTR Value 100n SYMBOL current 1344 -64 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName I1 SYMATTR Value PULSE(0 5 412m 100n) SYMBOL bridgerec -528 208 R0 SYMATTR InstName X1 TEXT -98 560 Left 0 !.tran 0 500m 0 40u startup TEXT -48 480 Left 0 !.include uc384x.lib TEXT 816 -96 Left 0 !k l1 l2 l3 1 TEXT 1416 504 Left 0 ;.ic V( VFb) =3D 0 TEXT -648 344 Left 0 ;.ic v(n001) =3D 200 RECTANGLE Normal 880 96 624 -128
Here is the uc3842 Symbol:
Version 4 SymbolType CELL RECTANGLE Normal -160 -160 160 160 WINDOW 0 8 -176 Left 0 WINDOW 3 8 176 Left 0 SYMATTR Value UC3845B SYMATTR Prefix X SYMATTR Description High Speed Current Mode Pulse Width Modulator PIN -160 -32 LEFT 8 PINATTR PinName COMP PINATTR SpiceOrder 1 PIN -160 -96 LEFT 8 PINATTR PinName FB PINATTR SpiceOrder 2 PIN 160 64 RIGHT 8 PINATTR PinName Isense PINATTR SpiceOrder 3 PIN -160 96 LEFT 8 PINATTR PinName Rt/Ct PINATTR SpiceOrder 4 PIN 0 160 BOTTOM 8 PINATTR PinName GND PINATTR SpiceOrder 5 PIN 160 -64 RIGHT 8 PINATTR PinName Output PINATTR SpiceOrder 6 PIN 0 -160 TOP 8 PINATTR PinName Vcc PINATTR SpiceOrder 7 PIN -160 32 LEFT 8 PINATTR PinName Vref PINATTR SpiceOrder 8